Copper-based metal polishing solution and method for manufacturing a semiconductor device

ABSTRACT

A copper-based metal polishing solution comprises a water-soluble organic acid capable of reaction with copper to form a copper complex compound which is unlikely to be dissolved in water and has a mechanical strength lower than that of copper. The polishing solution also contains polishing abrasive grains and water. The polishing solution of the particular composition does not dissolve at all copper or a copper alloy when a copper or copper alloy film is immersed in the polishing solution, and permits polishing the copper or copper alloy film at a practical rate in the polishing step.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a copper-based metal polishing solutionand a method for manufacturing a semiconductor device.

2. Description of the Related Art

Formation of a wiring layer is included in the process of manufacturinga semiconductor device, and an etch-back technique is employed foreliminating stepped portions from a surface of the wiring layer. Theetch-back technique comprises the steps of forming grooves conformingwith a pattern of the wiring layer in an insulating film covering asubstrate of a semiconductor substrate, depositing a copper film on theinsulating film including the trenches, polishing the copper film with apolishing solution, and selectively allowing the copper film to remainwithin the trenches to form a buried wiring layer.

It was customary in the past to use a polishing solution prepared bydispersing polishing abrasive grains such as a colloidal silica in purewater. In the conventional technique, the polishing solution is suppliedinto a polishing pad included in a polishing apparatus, and the copperfilm formed on the substrate surface is polished, with a predeterminedload applied to the polishing pad. In the conventional technique,however, a mechanical polishing, which involves the polishing abrasivegrains and the polishing pad, is simply applied to the copper film, withthe result that the polishing rate was as low as only 10 nm/min.

Other types of polishing solutions for a copper film or a copper alloyfilm are disclosed in, for example, "J. Electrochem. Soc., Vol. 138, No.11, 3460 (1991)", "VMIC Conference, ISMIC-101/92/0156 (1992)" and "VMICConference, ISMIC-102/93/0205 (1993)". To be more specific, disclosed inthese publications are polishing solutions each consisting of a slurryof an amine-based colloidal silica or a slurry containing K₃ Fe(CN)₆, K₄(CN)₆, or Co(NO₃)₂. However, the polishing solution disclosed in any ofthese publications gives rise to the difficulty that there is nodifference in the etching rate of the copper film between the immersingstep and the polishing step. As a result, the copper wiring layer withinthe trench is further etched with the polishing solution when the wiringlayer is brought into contact with the polishing solution after theetch-back step. It follows that the upper surface of the copper wiringlayer within the trench is positioned lower than the upper surface ofthe insulating film. In other words, it is difficult to form the wiringlayer flush with the insulating film, leading to an impaired surfacesmoothness. What should also be noted is that the copper wiring layerburied in this fashion in the insulating film exhibits a resistivityhigher than that of the copper wiring layer buried in the insulatingfilm such that the upper surface of the wiring layer is flush with theupper surface of the insulating film.

Japanese Patent Disclosure (Kokai) No. 7-233485 discloses an additionalcopper-based metal polishing solution prepared by adding at least onekind of an organic acid selected from the group consisting ofaminoacetic acid and amidosulfuric acid, and an oxidizing agent towater. Where elemental copper or a copper alloy is immersed in thecopper-based metal polishing solution disclosed in this publication, theetching rate of the copper or copper alloy is very low. However, wherethe copper or copper alloy is subjected to a polishing treatment withthe particular polishing solution, the etching rate of the copper orcopper alloy is several to scores of times as high as that in the caseof the immersion in the polishing solution. To be more specific, ifaminoacetic acid included in the polishing solution disclosed in theabove-noted publication reacts with hydrated copper, a complex compoundsoluble in water is formed, as shown below:

    Cu(H.sub.2 O).sub.4.sup.2+ +2H.sub.2 NCH.sub.2 COOH→Cu(H.sub.2 NCH.sub.2 COOH).sub.2 +4H.sub.2 O+2H.sup.+

It should be noted that copper does not react with a mixture ofaminoacetic acid and water. The reaction given above proceeds in adirection denoted by the arrow, if an oxidizing agent, e.g., hydrogenperoxide, is added to the reaction system, resulting in an etching ofcopper. If, for example, a copper film is immersed in the polishingsolution, an oxide film is formed on the surface of the copper film soas to suppress the etching (dissolving) of the copper film. On the otherhand, if the copper film is polished with a polishing pad containing thepolishing solution, the oxide film formed on the film surface ismechanically removed by the polishing pad so as to expose the purecopper to the surface. It follows that the copper film is rapidlypolished chemically by the functions of the aminoacetic acid andhydrogen peroxide contained in the polishing solution. It should benoted in this connection that the copper or copper alloy film tends tobe dissolved in the polishing solution to some extent during a shortperiod immediately after the polishing treatment and before formation ofan oxide film on the film surface.

The prior art exemplified above, i.e., Japanese Patent Disclosure No.7-233485, also discloses a method for manufacturing a semiconductordevice in which a buried wiring layer made of copper or a copper alloyis formed by an etch-back technique using the copper-based metalpolishing solution described above.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a copper-based metalpolishing solution which does not dissolve at all a copper or copperalloy film immersed therein and which permits the copper or copper alloyfilm to be polished at a practical rate in the polishing step.

Another object is to provide a method for manufacturing a semiconductordevice, in which at least one member selected from the group consistingof a trench and an opening is formed in an insulating film on asemiconductor substrate, a wiring material selected from the groupconsisting of elemental copper and a copper alloy deposited on theinsulating film can be etched back within short time period to form aburied wiring layer whose surface is level with the surface of theinsulating film.

According to a first aspect of the present invention, there is provideda copper-based metal polishing solution, comprising a water-solubleorganic acid capable of reaction with copper to form a copper complexcompound which is unlikely to be dissolved in water and has a mechanicalstrength lower than that of copper, polishing abrasive grains and water.

According to a second aspect of the present invention, there is provideda method for manufacturing a semiconductor device, comprising the stepsof:

forming at least one member selected from the group consisting of atrench and an opening, the groove and opening conforming in shape with awiring layer, in an insulating film formed on a semiconductor substrate;

depositing a wiring material selected from the group consisting ofelemental copper and a copper alloy on the insulating film having atleast one of the trench and opening formed therein; and

polishing the deposited wiring material film until a surface of theinsulating film is exposed by using a polishing solution comprising awater-soluble organic acid capable of reaction with copper to form acopper complex compound which is unlikely to be dissolved in water andhas a mechanical strength lower than that of copper, polishing abrasivegrains and water, thereby forming a buried wiring layer in theinsulating film such that surfaces of the wiring layer and theinsulating film are level with each other.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a cross sectional view schematically showing the constructionof a polishing apparatus used in the polishing step included in themethod of the present invention;

FIG. 2 is a graph showing the relationship between the polishing rateand the temperature of the polishing solution, covering the cases wherea copper film formed on a substrate was subjected to a polishingtreatment using a polishing solution of the present invention or aconventional polishing solution containing polishing abrasive grains;

FIG. 3 is a graph showing the relationship between the polishing rate ofa copper film and the 2-quinoline carboxylic acid content of a polishingsolution consisting of 2-quinoline carboxylic acid, hydrogen peroxide,polishing abrasive grains and water;

FIG. 4 is a graph showing the relationship between the polishing rate ofa copper film and the hydrogen peroxide content of a polishing solutionconsisting of 2-quinoline carboxylic acid, hydrogen peroxide, polishingabrasive grains and water;

FIGS. 5A to 5C are cross sectional views collectively showing how acopper film having projections and recesses on the surface will bechanged when subjected to a polishing treatment with a polishingapparatus, using a polishing solution consisting of 2-quinolinecarboxylic acid, hydrogen peroxide, polishing abrasive grains and water;

FIG. 6 is a graph showing the relationship between the polishing rate ofa copper film and the pH value of a polishing solution;

FIG. 7 is a graph showing the relationship between the polishing rate ofa copper film, a P-SiN film, i.e., a silicon nitride film formed byplasma CVD, and a SiO₂ film and an amount of a surfactant (sodiumdodecyl sulfate) added to the polishing solution;

FIG. 8 is a graph showing the relationship between the polishing rate ofa copper film, a P-SiN film and a SiO₂ film and the kinds of surfactantsadded to the polishing solution;

FIGS. 9A to 9C are cross sectional views collectively showing a methodof manufacturing a semiconductor device according to a first embodiment(Example 1) of the present invention;

FIGS. 10A to 10C are cross sectional views collectively showing a methodof manufacturing a semiconductor device according to a second embodiment(Example 5) of the present invention; and

FIGS. 11A to 11F are cross sectional views collectively showing a methodof manufacturing a semiconductor device according to a third embodiment(Example 6) of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Let us describe in detail a copper-based metal polishing solution of thepresent invention.

Specifically, the copper-based metal polishing solution of the presentinvention comprises a water-soluble organic acid capable of reactionwith copper to form a copper complex compound which is unlikely to bedissolved in water and has a mechanical strength lower than that ofcopper, polishing abrasive grains and water.

The organic acid used in the present invention includes, for example,2-quinoline carboxylic acid (quinaldinic acid), 2-pyridine carboxylicacid, 2,6-pyridine carboxylic acid, and quinones. It is desirable forthe polishing solution to contain at least 0.1% by weight of theparticular organic acid. If the organic acid content of the polishingsolution is lower than 0.1% by weight, it is difficult to form in asufficiently large amount a copper complex compound which ismechanically weaker than the elemental copper on the surface of a copperfilm or a copper alloy film, making it difficult to increasesufficiently the polishing rate of the copper or copper alloy film inthe polishing step. Preferably, the organic acid content of thepolishing solution should fall within a range of between 0.3 and 1.2% byweight.

The polishing abrasive grains contained in the polishing solution of thepresent invention are formed of at least one material selected from thegroup consisting of silica, zirconia, cerium oxide and alumina.Particularly, it is desirable to use alumina grains having a hardnessadapted for the polishing as a base material of the polishing abrasivegrains. To be more specific, it is desirable for the polishing abrasivegrains to consist of alumina grains singly or of a mixture of aluminagrains and silica grains such as colloidal silica. Also, the polishingabrasive grains should desirably be spherical and have an averagediameter of 0.02 to 0.1 μm. Where a copper film or a copper alloy filmis subjected to a polishing treatment with a polishing solutioncontaining polishing abrasive grains having such an average graindiameter, it is possible to suppress damage done to the surface of thecopper or copper alloy film. It is particularly desirable to useγ-alumina for forming spherical polishing abrasive grains becausespherical grains can be prepared without difficulty in the case of usingγ-alumina.

It is desirable for the polishing solution of the present invention tocontain 1 to 20% by weight of the polishing abrasive grains. If thecontent of the polishing abrasive grains is lower than 1% by weight, itis difficult to obtain sufficiently the effect produced by the polishingabrasive grains. On the other hand, the polishing abrasive grains addedin an amount exceeding 20% by weight cause the polishing solution to beunduly viscous, making it difficult to handle smoothly the polishingsolution. Preferably, the content of the polishing abrasive grainsshould fall within a range of between 2 and 10% by weight.

The polishing solution of the present invention may also contain apromoter for forming a copper complex compound including, for example,oxidizing agents such as hydrogen peroxide (H₂ O₂), and sodiumhypochlorite (NaClO). It is desirable for the polishing solution of thepresent invention to contain the oxidizing agent in an amount at least10 times as much by weight as that of the organic acid. Where the amountof the oxidizing agent is less than 10 times as much by weight as thatof the organic acid, it is impossible to promote sufficiently formationof a copper complex compound on the surface of the copper or copperalloy film. The amount of the oxidizing agent should preferably be atleast 30 times as much, and more preferably 50 times as much, by weightas that of the organic agent.

The polishing solution of the present invention may also contain apH-adjusting agent such as an alkalizing agent including, for example,potassium hydroxide or choline.

The polishing solution of the present invention may further containnonionic, amphoteric, anionic, and cationic surfactants. The nonionicsurfactants used in the present invention include, for example,polyethylene glycol phenyl ether and ethylene glycol fatty acid ester.The amphoteric surfactants include, for example, imidazolibetain. Theanionic surfactants include, for example, sodium dodecylsulfate.Further, the cationic surfactants include, for example, stearintrimethyl ammonium chloride. It is desirable to use these surfactants inthe form of a mixture of at least two compounds. The polishing solutionof the present invention further containing surfactants permitsimproving the selectivity of polishing between a copper or copper alloyfilm and an insulating film such as a SiN film or a Si₂ O film, asdescribed in detail herein later.

It is desirable to use the surfactant in an amount of 1 mol per liter ofthe polishing solution. Where the amount of the surfactant is less than1 mol per liter of the polishing solution, it is difficult to improvethe selectivity of polishing between the copper or copper alloy film andthe insulating film such as a SiO₂ film in the polishing step. Morepreferably, the amount of the surfactant should fall within the range ofbetween 10 and 100 mols per liter of the polishing solution.

FIG. 1 shows a polishing apparatus used for polishing a copper orcopper-alloy film formed on a substrate by using a copper-based metalpolishing solution of the present invention. As shown in the drawing, aturntable 1 is covered with a polishing pad 2 made of, for example, acloth. A pipe 3 for supplying a polishing solution is arranged above thepolishing pad 2. Further, a substrate holder 5 having a supporting shaft4 mounted to the upper surface thereof is also arranged above thepolishing pad 2. The substrate holder 5 is rotatable and movable in avertical direction. A substrate 6 is held by the holder 5 such that thepolishing surface, e.g., a copper film, of the substrate 6 is in contactwith the polishing pad 2. Under this condition, a polishing solution 7of the composition described previously is supplied through the pipe 3onto the polishing pad 2. In this step, a predetermined load is appliedto the substrate 6 toward the polishing pad 2 by using the supportingshaft 4 of the polishing apparatus. Further, the holder 5 and theturntable 1 are rotated in opposite directions so as to polish thecopper film formed on the substrate.

To reiterate, the copper-based metal polishing solution of the presentinvention comprises a water-soluble organic acid capable of reactionwith copper to form a copper complex compound which is unlikely to bedissolved in water and has a mechanical strength lower than that ofcopper, polishing abrasive grains and water. As a result, the copper orcopper alloy film is not dissolved at all when the film is immersed inthe polishing solution, making it possible to polish the copper orcopper alloy film at a practical polishing rate. Incidentally, the term"practical polishing rate" referred to above denotes a polishing rate atleast 3 times as high as that in the case of using a conventionalpolishing solution containing polishing abrasive grains alone.

To be more specific, the organic acid contained in the polishingsolution of the present invention, e.g., 2-quinoline carboxylic acid,reacts with a copper hydrate (copper ion) to form a copper complexcompound which is unlikely to be dissolved in water, as shown by thereaction formula given below: ##STR1##

The copper complex compound formed on the surface of the copper orcopper alloy film by the reaction given above is not dissolved in water,and has a mechanical strength lower than that of the copper or copperalloy. It follows that the copper complex compound can be removed easilyby the polishing treatment.

Where the polishing solution further contains a promoter such as anoxidizing agent for forming the copper complex compound, formation ofthe copper complex compound by the reaction given above is promoted,with the result that the copper or copper alloy film can be polished ata polishing rate at least 5 times as high as that in the case of using aconventional polishing solution containing the polishing abrasive grainsalone.

FIG. 2 is a graph showing the relationship between the polishing rateand the temperature of the polishing solution, covering the cases wherea copper film formed on a substrate was subjected to a polishingtreatment using a polishing solution of the present invention or aconventional polishing solution containing polishing abrasive grains.The polishing solution of the present invention contained 0.3% by weightof an organic acid, e.g., 2-quinoline carboxylic acid, 16.7% by weightof a promoter for forming a copper complex compound, e.g., hydrogenperoxide, 4.0% by weight of colloidal silica, and water. Line a in FIG.2 covers the use of the polishing solution of the present invention,with line b covering the use of the conventional polishing solution. Thepolishing apparatus shown in FIG. 1 was used for performing thepolishing treatment. Specifically, a substrate having a copper filmformed on a surface was held by the substrate holder 5 such that thecopper film was in contact with the polishing pad 2, i.e., SUBA 800,which is a trade name of a polishing pad manufactured by Rhodel NitterInc. Under this condition, a load of 300 g/cm² was applied to thesubstrate toward the polishing pad 2 via the supporting shaft 4.Further, the polishing solution was supplied through the pipe 3 onto thepolishing pad 2 at a rate of 12.5 ml/min while rotating the turntable 1and the holder 5 in opposite directions at a speed of 100 rpm so as toapply a polishing treatment to the copper film formed on the surface ofthe substrate. As apparent from FIG. 2, the polishing rate of the copperfilm in the case of using the polishing solution of the presentinvention (line a) was found to be about 6 times as high as that in thecase of using the conventional polishing solution containing polishingabrasive grains alone (line b).

FIG. 3 is a graph showing the relationship between the polishing rate ofa copper film and the 2-quinoline carboxylic acid content of a polishingsolution consisting of varied amounts of 2-quinoline carboxylic acid,16.7% by weight of hydrogen peroxide, polishing abrasive grainsconsisting of 1.3% by weight of γ-alumina grains and 4.0% by weight ofcolloidal silica grains, and water. The polishing treatment wasperformed as described above in conjunction with FIG. 2 using thepolishing apparatus shown in FIG. 1. As apparent from FIG. 3, thepolishing rate of the copper film is increased with increase in the2-quinoline carboxylic acid content of the polishing solution.

FIG. 4 is a graph showing the relationship between the polishing rate ofa copper film formed on a substrate and the hydrogen peroxide content ofa polishing solution consisting of 0.3% by weight of 2-quinolinecarboxylic acid, varied amount of hydrogen peroxide, polishing abrasivegrains formed of a mixture of 1.3% by weight of γ-lumina grains and 4.0%by weight of colloidal silica grains, and water. The polishing treatmentwas performed as already described in conjunction with FIG. 2 by usingthe polishing apparatus shown in FIG. 1. As apparent from FIG. 4, thepolishing rate of the copper film was only about 51 nm/min in the casewhere hydrogen peroxide was not contained at all in the polishingsolution. It is also seen that the polishing rate was increased withincrease in the hydrogen peroxide content of the polishing solution,reaching a polishing rate of about 90 nm/min where the hydrogen peroxidecontent of the polishing solution exceeded 9% by weight. It isconsidered reasonable to understand that the hydrogen peroxide containedin the polishing solution serves to promote formation of the coppercomplex compound such that the copper or copper alloy film exposed tothe outside in the mechanical polishing process performed by thepolishing pad and the polishing abrasive grains contained in thepolishing solution is allowed to promptly form the brittle coppercomplex compound in accordance with the reaction formula givenpreviously.

As a matter of fact, a copper film 12 having projections and recesses onthe surface was formed on a surface of a substrate 11, as shown in FIG.5A and, then, immersed in the polishing solution having a high polishingrate, which is shown in FIG. 4, for 3 minutes. To reiterate, thepolishing solution contained 0.3% by weight of 2-quinoline carboxylicacid, 1.3% by weight of γ-alumina grains, 4.0% by weight of colloidalsilica grains, and 16.7% by weight of hydrogen peroxide. As a result, acopper complex compound layer 13 was formed on the surface of the copperfilm 12, as shown in FIG. 5B. After the immersion in the polishingsolution, the surface of the copper film 12 was analyzed by XPS (X-rayphotoelectron spectroscopy). A large amount of carbon was detected onthe copper film surface, though the copper amount detected was verysmall. Further, the thickness of the copper complex compound layer wasfound to be about 20 nm when measured by AES (Auger electronspectroscopy).

The copper film 12 having the copper complex compound layer 13 formedthereon as shown in FIG. 5B was polished by the polishing pad includedin the polishing apparatus shown in FIG. 1, using a polishing solutionof the composition described above. As a result, the copper complexcompound layer 13 formed on the projected portion of the copper film 12was mechanically polished without difficulty by the polishing pad so asto expose the pure copper film 12 to the outside, as shown in FIG. 5C.The surface of the copper film immediately after the polishing wasanalyzed by XPS (X-ray photoelectron spectroscopy), with the result thatcopper alone, which was scarcely oxidized, was detected. It isconsidered reasonable to understand that, in the process of thepolishing treatment, the polishing of the copper film surface proceedssuch that a copper complex compound layer having a mechanical strengthlower than that of the copper film is formed on the surface of thecopper film and the copper complex compound layer thus formed ismechanically removed by the polishing pad.

Incidentally, the polishing solution of the present invention consistingof 2-quinoline carboxylic acid, polishing abrasive grains and waterexhibits a polishing rate at least 3 times as high as that exhibited bythe conventional polishing solution which does not contain 2-quinolinecarboxylic acid, as apparent from the comparison between FIG. 3 with noaddition of 2-quinoline carboxylic acid (conventional polishingsolution) and FIG. 4 with no addition of hydrogen peroxide (presentinvention). To be more specific, the copper polishing rate with noaddition of 2-quinoline carboxylic acid shown in FIG. 3 was only about15 nm/min in contrast to about 51 nm/min achieved by the polishingsolution of the present invention, with no addition of hydrogenperoxide, shown in FIG. 4.

It should be noted that the polishing solution of the present inventiondoes not dissolve at all copper or a copper alloy when a copper orcopper alloy film is immersed therein, and permits polishing a copper orcopper alloy film at a practical polishing rate, which is at least 3times as high as that achieved by the conventional polishing solutioncontaining polishing abrasive grains. It follows that the polishingsolution of the present invention makes it possible to avoid the problemthat the copper etching rate is changed by, for example, the timing ofsupplying a polishing solution in the step of the polishing treatment.In addition, the polishing treatment can be performed easily in the caseof using the polishing solution of the present invention.

It is important to note that, where the polishing apparatus shown inFIG. 1 is used for polishing the copper film formed on the substratesurface, the copper film is polished only when the polishing pad is incontact with the copper film under a predetermined load. In other words,the polishing is stopped immediately after the polishing pad is movedaway from the copper film, making it possible to prevent a so-calledover-etching, i.e., the phenomenon that the copper film is furtheretched after completion of the polishing treatment.

In the polishing step of the copper film 12 having projections andrecesses as shown in FIG. 5C, etching does not proceed from the sidesurface. Since the etching proceeds from only the upper surface of theprojection in contact with the polishing pad, it is highly effective toemploy the technical idea of the present invention in the etch-backtechnique described herein later. Further, the surface of the copperfilm after the polishing treatment is brought into contact with thepolishing solution, with the result that a layer of the particularcopper complex compound is formed on the copper film surface. However,since the copper complex compound layer is as thin as only 20 nm, thecopper film can be prevented from being unduly thinned in the step ofremoving the copper complex compound layer to expose the surface of thepure copper to the outside.

The polishing solution of the present invention may further contain analkalizing agent such as choline so as to adjust the pH value and, thus,to control the polishing rate of the copper or copper alloy film. FIG. 6is a graph showing how the polishing rate of a copper film formed on asubstrate is affected by the pH value of the polishing solution,covering the case where the copper film was subjected to a polishingtreatment using a polishing solution containing 0.3% by weight of2-quinoline carboxylic acid, 1.3% by weight of γ-alumina grains, 4.0% byweight of colloidal silica grains, and 16.7% by weight of hydrogenperoxide. Choline was added to the polishing solution to control the pHvalue of the solution within a range of between 4 and 9.5. FIG. 6clearly shows that the polishing rate of the copper film is decreasedwith increase in the pH value. Particularly, the polishing rate ismarkedly lowered, if the pH value exceeds 8.

The polishing solution of the present invention may further containnonionic, amphoteric, anionic or cationic surfactant so as to improvethe polishing selectivity between the copper or copper alloy film andthe insulating film such as a SiO₂ film. FIG. 7 is a graph showing howthe polishing rate of a copper film, a silicon nitride film formed byplasma CVD (P-SiN film), or a SiO₂ film formed on a substrate isaffected by the concentration of sodium dodecyl sulfate (SDS), which isan anionic surfactant, covering the case where the copper film or thelike was subjected to a polishing treatment using a polishing solutioncontaining 0.3% by weight of 2-quinoline carboxylic acid, 1.3% by weightof γ-alumina grains, 4.0% by weight of colloidal silica grains, 16.7% byweight of hydrogen peroxide, and varied amount of SDS. Curve A in FIG. 7denotes the change in the polishing rate of the copper film, with curvesB and C denoting the changes in the polishing rates of the P-SiN filmand the SiO₂ film, respectively. FIG. 7 shows that the polishing rate ofthe copper film is increased with increase in the SDS concentration(curve A). On the other hand, the polishing rates of the P-SiN film andthe SiO₂ film are decreased with increase in the SDS concentration. Itis seen that the polishing rate of each of the P-SiN film and the SiO₂film is lowered to substantially zero, when the SDS concentration isincreased to reach 10 mmol/liter. It follows that the polishingselectivity between the copper film and the insulating film such as theP-SiN film or SiO₂ film can be improved by controlling the amount of SDSadded to the polishing solution. The polishing selectivity can beimproved by the addition of not only the anionic surfactant of SDS butalso the amphoteric, cationic and nonionic surfactants, as shown in FIG.8.

As described above, 2-quinoline carboxylic acid contained in thepolishing solution of the present invention reacts with copper to form acopper complex compound which is unlikely to be dissolved in water andhas a mechanical strength lower than that of copper. In addition, otherwater-soluble organic acids such as 2-pyridine carboxylic acid,2,6-pyridine carboxylic acid, and quinone can also be usedsatisfactorily in place of 2-quinoline carboxylic acid. In the case ofusing any of these water-soluble organic acids, a copper or copper alloyfilm is not dissolved at all when immersed in the polishing solutioncontaining the particular organic acid, and the copper or copper alloyfilm can be polished at a practical polishing rate.

The present invention also provides a method for manufacturing asemiconductor device, comprising the steps of:

forming at least one member selected from the group consisting of atrench and an opening, the trench and opening conforming in shape with awiring layer, in an insulating film formed on a semiconductor substrate;

depositing a wiring material selected from the group consisting ofelemental copper and a copper alloy on the insulating film having atleast one of the trench and opening formed therein; and

polishing the deposited wiring material film until a surface of theinsulating film is exposed by using a polishing solution comprising awater-soluble organic acid capable of reaction with copper to form acopper complex compound which is unlikely to be dissolved in water andhas a mechanical strength lower than that of copper, polishing abrasivegrains and water, thereby forming a buried wiring layer in theinsulating film such that surfaces of the wiring layer and theinsulating film are level with each other.

The insulating film formed on the semiconductor substrate includes, forexample, a silicon oxide film, a boron-added glass film (BPSG film), anda phosphorus-added glass film (PSG film). The insulating film may becovered with a polishing stopper film made of, for example, siliconnitride, carbon, alumina, boron nitride, or diamond.

The copper alloy used in the present invention as a wiring materialincludes, for example, a Cu--Si alloy, a Cu--Al alloy, a Cu--Si--Alalloy and a Cu--Ag alloy. The wiring material film made of copper orcopper alloy can be deposited by means of, for example, sputtering,vapor deposition, or vacuum vapor deposition.

The organic acid content of the polishing solution should desirably fallwithin the range described previously in conjunction with thecopper-based metal polishing solution of the present invention. Thepolishing abrasive grains contained in the polishing solution include,for example, alumina grains, silica grains, cerium oxide grains andzirconia grains. In preparing the polishing abrasive grains, it isdesirable to use as a base material alumina grains having a hardnessadapted for the polishing. To be more specific, it is desirable to usealumina grains alone or a mixture of alumina grains and silica grainssuch as colloidal silica grains for preparing the polishing abrasivegrains.

The polishing abrasive grains should desirably be spherical orsubstantially spherical and should desirably have an average graindiameter of 0.02 to 0.1 μm. Where the polishing solution containspolishing abrasive grains defined in the present invention, it ispossible to suppress damage done to the surface of the copper or copperalloy film. It is particularly desirable to use γ-alumina grains as thepolishing abrasive grains because spherical γ-alumina grains can bemanufactured without difficulty. Further, the polishing abrasive grainsshould be contained in the polishing solution in an amount of 1 to 20%by weight, preferably, 2 to 7% by weight.

It is also possible for the polishing solution to contain a promotor forforming a copper complex compound. Oxidizing agents such as hydrogenperoxide (H₂ O₂), and sodium hypochlorite (NaClO) can be used as such apromotor. The amount of the oxidizing agent should be at least 10 timesas much by weight as the organic acid contained in the polishingsolution. Where the amount of the oxidizing agent is less than 10 timesas much by weight as the amount of the organic acid, the oxidizing agentfails to promote sufficiently the formation of the copper complexcompound on the surface of the copper or copper alloy film. Preferably,the oxidizing agent should be used in an amount at least 30 times, andmore preferably, at least 50 times as much by weight as the amount ofthe organic acid contained in the polishing solution.

It is also possible for the polishing solution to contain a pHvalue-controlling agent such as alkalizing agents including, forexample, potassium hydroxide and trimethyl ammonium hydroxide.

Further, it is also possible for the polishing solution used in themethod of the present invention for manufacturing a semiconductor deviceto contain nonionic, amphoteric, anionic and/or cationic surfactants.The nonionic surfactants used in the present invention include, forexample, polyethylene glycol phenyl ether and ethylene glycol fatty acidester. The amphoteric surfactants used in the present invention include,for example, imidazolibetaine. The anionic surfactants used in thepresent invention include, for example, sodium dodecyl sulfate. Further,the cationic surfactants used in the present invention includes, forexample, stearin trimethyl ammonium chloride. These surfactants can beused singly or in the form of a mixture of a plurality of differentsurfactants.

The polishing apparatus shown in FIG. 1 can be used for applying apolishing treatment to the semiconductor substrate having a wiringmaterial film deposited thereon. In performing a polishing treatment byusing the polishing apparatus shown in FIG. 1, the load applied to thepolishing pad through the semiconductor substrate held by a substrateholder is determined appropriately in view of the composition of thepolishing solution used. Where the polishing solution consists of, forexample, 2-quinoline carboxylic acid, polishing abrasive grains andwater, it is desirable for the load to fall within a range of between 50g/cm² and 1000 g/cm².

The method of the present invention for manufacturing a semiconductordevice may also comprise the step of forming a barrier layer in theinsulating film having at least one member selected from the groupconsisting of a trench and an opening formed therein before the step ofdepositing a wiring material film. In the case of forming such a barrierlayer, it is possible to form a buried wiring layer surrounded by thebarrier layer in at least one of the trench and the opening by thesubsequent step of depositing a wiring material film such as a copperfilm, followed by etch back. As a result, diffusion of copper, i.e., thewiring material, into the insulating film can be inhibited by thebarrier layer, making it possible to prevent the semiconductor substratefrom being contaminated by copper. The barrier layer should be formedof, for example, TiN, Ti, Nb, W or CuTa alloy, and should desirably havea thickness falling within a range of between 15 nm and 50 nm.

To reiterate, the method of the present invention for manufacturing asemiconductor substrate comprises the steps of forming at least onemember selected from the group consisting of a trench and an opening,the trench and opening conforming in shape with a wiring layer, in aninsulating film formed on a semiconductor substrate, depositing a wiringmaterial selected from the group consisting of elemental copper and acopper alloy on the insulating film having at least one of the trenchand opening formed therein, and polishing the deposited wiring materialfilm until a surface of the insulating film is exposed by using apolishing solution comprising a water-soluble organic acid capable ofreaction with copper to form a copper complex compound which is unlikelyto be dissolved in water and has a mechanical strength lower than thatof copper, polishing abrasive grains and water, thereby forming a buriedwiring layer in the insulating film such that surfaces of the wiringlayer and the insulating film are level with each other. Of course, thewiring layer is formed within the trench or opening formed in the firststep. Also, the polishing apparatus as shown in FIG. 1 is used forapplying the polishing treatment to the deposited wiring material film.As already described, the polishing solution used in the presentinvention does not dissolve at all a copper or copper alloy film whenthe film is immersed in the polishing solution. In addition, thepolishing solution permits polishing the copper or copper alloy film ata practical polishing rate, i.e., at least 3 times as high as thepolishing rate achieved by the conventional polishing solutioncontaining polishing abrasive grains alone. Particularly, where thepolishing solution contains a promotor for forming a copper complexcompound such as an oxidizing agent, the copper or copper alloy film canbe polished at a polishing rate at least 5 times as high as thepolishing rate achieved by the conventional polishing solutioncontaining polishing abrasive grains alone. As a result, the uppersurface alone of the wiring material film (e.g., a copper film) can bepolished so as to achieve a so-called etch-back. It follows that it ispossible to form a buried wiring layer made of copper or a copper alloyin at least one of a trench and an opening formed in the insulating filmsuch that the upper surface of the buried wiring layer is flush with thesurface of the insulating film. What should also be noted is that theresultant wiring layer is prevented from being etched when the wiringlayer is brought into contact with the polishing solution after theetch-back step, because the polishing solution used in the presentinvention does not dissolve at all copper or a copper alloy, as alreadydescribed. It follows that the method of the present invention makes itpossible to manufacture a semiconductor device comprising a buriedwiring layer of a high precision having a flat surface.

The surface of the buried wiring layer formed in the insulating film isbrought into contact with the polishing solution, resulting in formationof a copper complex compound layer. However, since the copper complexcompound layer thus formed is as thin as only 20 nm, the buried wiringlayer is prevented from being unduly thinned in the step of exposing thepure copper surface by removing the copper complex compound layer.

Further, the polishing solution used in the present invention containsspherical or substantially spherical polishing abrasive grains, with theresult that the wiring material film is prevented from being cracked ordamaged in the etch-back step. It follows that it is possible to form aburied wiring layer of a high reliability in the insulating film. Itshould also be noted that, if the insulating film is covered in advancewith a polishing stopper film made of, for example, silicon nitride,carbon, alumina, boron nitride or diamond, the insulating film can beprevented from being polished in the etch back step of the wiringmaterial film. As a result, thinning of the insulating film can besuppressed, making it possible to manufacture a semiconductor devicehaving a high breakdown voltage.

Further, where the polishing solution contains nonionic, amphoteric,anionic and/or cationic surfactants, the polishing selectivity betweenthe wiring material film made of copper or a copper alloy and theinsulating film made of, for example, SiO₂ can be improved in the etchback step, making it possible to prevent the insulating film from beingthinned. It follows that the resultant semiconductor device is enabledto exhibit a high breakdown voltage. In addition, where the polishingsolution contains such a surfactant, the contaminants remaining on theinsulating film such fine wiring material and organic materials can beremoved easily in a washing step after the etch back step, making itpossible to manufacture a semiconductor device having a clean surface,i.e., an insulating film having organic materials and residual wiringmaterial removed from the surface thereof.

Let us describe preferred Examples of the present invention withreference to the accompanying drawings.

EXAMPLE 1

A SiO₂ film 22 having a thickness of, for example, 1000 nm was formed asan interlayer insulating film by a CVD method on the surface of asilicon substrate 21 having diffusion layers (not shown) such as sourceand drain layers formed in a surface region thereof, as shown in FIG.9A. Then, a plurality of trenches 23 each having a depth of 500 nm andconforming in shape with a wiring layer were formed in the SiO₂ film 22by a photoetching technique. After formation of these trenches 23, abarrier layer 24 made of TiN and having a thickness of 15 nm and acopper film 25 having a thickness of 600 nm were formed successively inthis order by a sputtering technique on the surface of the SiO₂ film 22including the trenches 23, as shown in FIG. 9B.

The substrate 21 having the barrier layer 24 and the copper film 25formed thereon as shown in FIG. 9B was held by the substrate holder 5included in the polishing apparatus shown in FIG. 1 such that the copperfilm 25 was in contact with the polishing pad 2, i.e., SUBA 800 which isa trade name of a polishing pad manufactured by Rhodel Nitter Inc,included in the polishing apparatus. Under this condition, a load of 300g/cm² was applied via the supporting shaft 4 of the substrate holder 5to the substrate in contact with the polishing pad 2 disposed on theturntable 1, and the turntable 1 and the substrate holder 5 were rotatedin opposite directions each at a speed of 100 rpm. During the rotation,a polishing solution consisting of 0.3 wt % by weight of 2-quinolinecarboxylic acid, 1.4 wt % by weight of γ-alumina grains having anaverage grain diameter of 30 nm, 4.1 wt % by weight of colloidal silicagrains, and the balance of pure water was supplied through the supplypipe 3 onto the polishing pad 2 at a rate of 12.5 ml/min so as to polishthe copper film 25 and the barrier layer 24 deposited on thesemiconductor substrate 21 until the surface of the SiO₂ film 22 wasexposed to the outside. In this polishing step, etching of the copperfilm 25 was not recognized at all when the polishing solution wasbrought into contact with the copper film. Also, the polishing rateachieved by the polishing pad 2 was found to be about 51 nm/min. As aresult, the upper surfaces of the projections of the copper film 25 asshown in FIG. 9B, which were in a mechanical contact with the polishingpad 2, were preferentially polished first and, then, the exposed barrierlayer 24 was subsequently polished. In other words, a so-called etchback was achieved. Since the polishing was performed until the uppersurfaces of the projected portions of the SiO₂ 22 were exposed to theoutside, formed was a buried copper wiring layer 26 within the trench23, as shown in FIG. 9C. It is seen that the buried copper wiring layer26 was surrounded by the barrier layer 24, and that the upper surface ofthe buried copper wiring layer 26 was flush with the upper surface ofthe SiO₂ film 22.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copperwiring layer 26 was brought into contact with the polishing solution.However, the copper wiring layer 26 was found not to be etched at all.

EXAMPLE 2

A SiO₂ film having a thickness of, for example, 1000 nm was formed as aninterlayer insulating film by a CVD method on the surface of a siliconsubstrate having diffusion layers (not shown) such as source and drainlayers formed in a surface region thereof. Then, a plurality of trencheseach having a depth of 500 nm and conforming in shape with a wiringlayer were formed in the SiO₂ film by a photoetching technique. Afterformation of these trenches, a barrier layer made of TiN and having athickness of 15 nm and a copper film having a thickness of 600 nm wereformed successively in this order by a sputtering technique on thesurface of the SiO₂ film including the trenches.

The substrate having the barrier layer and the copper film formedthereon was held by the substrate holder 5 included in the polishingapparatus shown in FIG. 1 such that the copper film was in contact withthe polishing pad 2, i.e., SUBA 800, included in the polishingapparatus. Under this condition, a load of 300 g/cm² was applied via thesupporting shaft 4 of the substrate holder 5 to the substrate in contactwith the polishing pad 2 disposed on the turntable 1, and the turntable1 and the substrate holder 5 were rotated in opposite directions each ata speed of 100 rpm. During the rotation, a polishing solution consistingof 0.3% by weight of 2-quinoline carboxylic acid, 16.7% by weight ofhydrogen peroxide, 1.3% by weight of γ-alumina grains having an averagegrain diameter of 30 nm, 4.0% by weight of colloidal silica grains, andthe balance of pure water was supplied through the supply pipe 3 ontothe polishing pad 2 at a rate of 12.5 ml/min so as to polish the copperfilm and the barrier layer deposited on the silicon substrate until thesurface of the SiO₂ film was exposed to the outside. It should be notedthat the amount of hydrogen peroxide used was about 56 times as much byweight as the amount of 2-quinoline carboxylic acid used. In thispolishing step, etching of the copper film was not recognized at allwhen the polishing solution was brought into contact with the copperfilm. Also, the polishing rate achieved by the polishing pad was foundto be about 85 nm/min. As a result, the upper surfaces of theprojections of the copper film, which were in a mechanical contact withthe polishing pad, were preferentially polished first and, then, theexposed barrier layer was subsequently polished. In other words, aso-called etch back was achieved. Since the polishing was performeduntil the upper surfaces of the projected portions of the SiO₂ wereexposed to the outside, formed was a buried copper wiring layer withinthe trench. It should be noted that the buried copper wiring layer wassurrounded by the barrier layer, and that the upper surface of theburied copper wiring layer was flush with the upper surface of the SiO₂film.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copperwiring layer was brought into contact with the polishing solution.However, the copper wiring layer 26 was found not to be etched at all.

EXAMPLE 3

A SiO₂ film having a thickness of, for example, 1000 nm was formed as aninterlayer insulating film by a CVD method on the surface of a siliconsubstrate having diffusion layers (not shown) such as source and drainlayers formed in a surface region thereof. Then, a plurality of trencheseach having a depth of 500 nm and conforming in shape with a wiringlayer were formed in the SiO₂ film by a photoetching technique. Afterformation of these trenches, a barrier layer made of TiN and having athickness of 15 nm and a copper film having a thickness of 600 nm wereformed successively in this order by a sputtering technique on thesurface of the SiO₂ film including the trenches.

The substrate having the barrier layer and the copper film formedthereon was held by the substrate holder 5 included in the polishingapparatus shown in FIG. 1 such that the copper film was in contact withthe polishing pad 2, i.e., SUBA 800 referred to previously, included inthe polishing apparatus. Under this condition, a load of 300 g/cm² wasapplied via the supporting shaft 4 of the substrate holder 5 to thesubstrate in contact with the polishing pad 2 disposed on the turntable1, and the turntable 1 and the substrate holder 5 were rotated inopposite directions each at a speed of 100 rpm. During the rotation, apolishing solution consisting of 0.3% by weight of 2-quinolinecarboxylic acid, 16.7% by weight of hydrogen peroxide, 1.3% by weight ofγ-alumina grains having an average grain diameter of 30 nm, 4.0% byweight of colloidal silica grains, 10 mmol/liter of sodium dodecylsulfate, which is an anionic surfactant, and the balance of pure waterwas supplied through the supply pipe 3 onto the polishing pad 2 at arate of 12.5 ml/min so as to polish the copper film and the barrierlayer deposited on the silicon substrate until the surface of the SiO₂film was exposed to the outside. It should be noted that the amount ofhydrogen peroxide used was about 56 times as much by weight as theamount of 2-quinoline carboxylic acid used. In this polishing step,etching of the copper film was not recognized at all when the polishingsolution was brought into contact with the copper film. Also, thepolishing rate achieved by the polishing pad was found to be about 85nm/min. As a result, the upper surfaces of the projections of the copperfilm, which were in a mechanical contact with the polishing pad, werepreferentially polished first and, then, the exposed barrier layer wassubsequently polished. In other words, a so-called etch back wasachieved. Since the polishing was performed until the upper surfaces ofthe projected portions of the SiO₂ were exposed to the outside, formedwas a buried copper wiring layer within the trench. It should be notedthat the buried copper wiring layer was surrounded by the barrier layer,and that the upper surface of the buried copper wiring layer was flushwith the upper surface of the SiO₂ film.

As already described in conjunction with FIG. 7, an etching solutioncontaining a surfactant exhibits a high polishing selectivity. As amatter of fact, the SiO₂ film formed as an interlayer insulating filmwas prevented from being thinned in this Example because the polishingsolution used contained a surfactant as described above.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copperwiring layer was brought into contact with the polishing solution.However, the copper wiring layer was found not to be etched at all.

Further, an ultrasonic wave washing was applied by using pure water tothe silicon substrate having the buried wiring layer formed therein. Asa result, the residual copper particles, copper complex compoundparticles and organic material such as 2-quinoline carboxylic acid wereremoved from the substrate surface including the surface of the SiO₂film (interlayer insulating film) so as to clean the surface of the SiO₂film, etc.

As described above, a buried copper wiring layer having a thicknessequal to the depth of the trench formed in the interlayer insulatingfilm was formed in the interlayer insulating film in this Example. Whatshould be noted is that the upper surface of the buried copper wiringlayer was flush with the surface of the interlayer insulating film so asto make flat the surface of the silicon substrate after formation of thewiring layer. Further, the polishing solution used in the etch back stepfor forming the buried copper wiring layer contained a surfactant. Inaddition, the silicon substrate after formation of the buried copperwiring layer was subjected to washing with an ultrasonic wave using apure water. As a result, the surfactant contained in the polishingsolution permitted the surface of the interlayer insulating film to becleaned without difficulty so as to prepare a semiconductor device of ahigh reliability comprising a buried copper wiring layer of a lowresistivity inherent in copper.

EXAMPLE 4

A SiO₂ film having a thickness of, for example, 1000 nm was formed as aninterlayer insulating film by a CVD method on the surface of a siliconsubstrate having diffusion layers (not shown) such as source and drainlayers formed in a surface region thereof. Then, a plurality of trencheseach having a depth of 500 nm and conforming in shape with a wiringlayer were formed in the SiO₂ film by a photoetching technique. Afterformation of these trenches, a barrier layer made of TiN and having athickness of 15 nm and a copper film having a thickness of 600 nm wereformed successively in this order by a sputtering technique on thesurface of the SiO₂ film including the trenches.

The substrate having the barrier layer and the copper film formedthereon was held by the substrate holder 5 included in the polishingapparatus shown in FIG. 1 such that the copper film was in contact withthe polishing pad 2, i.e., SUBA 800, included in the polishingapparatus. Under this condition, a load of 300 g/cm² was applied via thesupporting shaft 4 of the substrate holder 5 to the substrate in contactwith the polishing pad 2 disposed on the turntable 1, and the turntable1 and the substrate holder 5 were rotated in opposite directions each ata speed of 100 rpm. During the rotation, a polishing solution consistingof 0.3% by weight of 2-quinoline carboxylic acid, 1.4% by weight ofγ-alumina grains having an average grain diameter of 30 nm, 4.1% byweight of colloidal silica grains, and the balance of pure water wassupplied through the supply pipe 3 onto the polishing pad 2 at a rate of12.5 ml/min so as to polish the copper film and the barrier layerdeposited on the silicon substrate until the surface of the SiO₂ filmwas exposed to the outside. In this polishing step, etching of thecopper film was not recognized at all when the polishing solution wasbrought into contact with the copper film. Also, the polishing rateachieved by the polishing pad was found to be about 30 nm/min. As aresult, the upper surfaces of the projections of the copper film, whichwere in a mechanical contact with the polishing pad, were preferentiallypolished first and, then, the exposed barrier layer was subsequentlypolished. In other words, a so-called etch back was achieved. Since thepolishing was performed until the upper surfaces of the projectedportions of the SiO₂ were exposed to the outside, formed was a buriedcopper wiring layer within the trench. It should be noted that theburied copper wiring layer was surrounded by the barrier layer, and thatthe upper surface of the buried copper wiring layer was flush with theupper surface of the SiO₂ film.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copperwiring layer 26 was brought into contact with the polishing solution.However, the copper wiring layer 26 was found not to be etched at all.

EXAMPLE 5

A SiO₂ film 22 having a thickness of, for example, 800 nm and a Si₃ N₄film 27 having a thickness of 200 nm and acting as a polishing stopperfilm were formed in this order, said SiO₂ film 22 and Si₃ N₄ film 27collectively forming an interlayer insulating film, by a CVD method onthe surface of a silicon substrate 21 having diffusion layers (notshown) such as source and drain layers formed in a surface regionthereof, as shown in FIG. 10A. Then, a plurality of trenches 23 eachhaving a depth of 500 nm and conforming in shape with a wiring layerwere formed to extend through the Si₃ N₄ film 27 to reach a middleregion of the SiO₂ film 22 by a photoetching technique. After formationof these trenches 23, a barrier layer 24 made of TiN and having athickness of 15 nm and a copper film 25 having a thickness of 600 nmwere formed successively in this order by a sputtering technique on thesurface of the Si₃ N₄ film 27 including the trenches 23, as shown inFIG. 10B.

The substrate having the barrier layer 24 and the copper film 25 formedthereon as shown in FIG. 10B was held by the substrate holder 5 includedin the polishing apparatus shown in FIG. 1 such that the copper film 25was in contact with the polishing pad 2, i.e., SUBA 800 referred topreviously, included in the polishing apparatus. Under this condition, aload of 300 g/cm² was applied via the supporting shaft 4 of thesubstrate holder 5 to the substrate in contact with the polishing pad 2disposed on the turntable 1, and the turntable 1 and the substrateholder 5 were rotated in opposite directions each at a speed of 100 rpm.During the rotation, a polishing solution consisting of 0.3% by weightof 2-quinoline carboxylic acid, 16.7% by weight of hydrogen peroxide,1.3% by weight of γ-alumina grains having an average grain diameter of30 nm, 4.0% by weight of colloidal silica grains, and the balance ofpure water was supplied through the supply pipe 3 onto the polishing pad2 at a rate of 12.5 ml/min so as to polish the copper film 25 and thebarrier layer 24 deposited on the semiconductor substrate 21 until thesurface of the Si₃ N₄ film 27 was exposed to the outside. It should benoted that the amount of hydrogen peroxide used was about 56 times asmuch by weight as the amount of 2-quinoline carboxylic acid used. Inthis polishing step, etching of the copper film 25 was not recognized atall when the polishing solution was brought into contact with the copperfilm. Also, the polishing rate achieved by the polishing pad 2 was foundto be about 100 nm/min. As a result, the upper surfaces of theprojections of the copper film 25 as shown in FIG. 10B, which were in amechanical contact with the polishing pad 2, were preferentiallypolished first and, then, the exposed barrier layer 24 was subsequentlypolished. In other words, a so-called etch back was achieved. Since thepolishing was performed until the upper surfaces of the projectedportions of the Si₃ N₄ 27 were exposed to the outside, formed was aburied copper wiring layer 26 within the trench 23, as shown in FIG.10C. It is seen that the buried copper wiring layer 26 was surrounded bythe barrier layer 24, and that the upper surface of the buried copperwiring layer 26 was flush with the upper surface of the Si₃ N₄ film 27.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copperwiring layer 26 was brought into contact with the polishing solution.However, the copper wiring layer 26 was found not to be etched at all.

What should also be noted is that the Si₃ N₄ film 27 acting as apolishing stopper film was included in the interlayer insulating film inthis Example. As a result, it was possible to suppress effectively thethinning of the interlayer insulating film in the etch back step,leading to production of a semiconductor device comprising an interlayerinsulating film exhibiting a high breakdown voltage.

EXAMPLE 6

A SiO₂ film 33 having a thickness of, for example, 1000 nm and acting asa first interlayer insulating film was formed by a CVD method on thesurface of a p-type silicon substrate 32 having an n⁺ -type diffusionlayer 31 formed in a surface region thereof, as shown in FIG. 11A. Then,an opening, i.e., a via hall 34 was formed through the SiO₂ film 33 toexpose the ⁺ -type diffusion layer 31 by a photoetching technique. Afterformation of the via hall 34, a barrier layer 35 made of TiN and havinga thickness of 20 nm and a copper film 36 having a thickness of 1100 nmwere formed successively in this order by a sputtering technique on thesurface of the SiO₂ film 33 including the via hall 34, as shown in FIG.11B.

The substrate having the barrier layer 35 and the copper film 36 formedthereon as shown in FIG. 11B was held by the substrate holder 5 includedin the polishing apparatus shown in FIG. 1 such that the copper film 36was in contact with the polishing pad 2, i.e., SUBA 800 referred topreviously, included in the polishing apparatus. Under this condition, aload of 300 g/cm² was applied via the supporting shaft 4 of thesubstrate holder 5 to the substrate in contact with the polishing pad 2disposed on the turntable 1, and the turntable 1 and the substrateholder 5 were rotated in opposite directions each at a speed of 100 rpm.During the rotation, a polishing solution consisting of 0.3% by weightof 2-quinoline carboxylic acid, 16.7% by weight of hydrogen peroxide,1.3% by weight of γ-alumina grains having an average grain diameter of30 nm, 4.0% by weight of colloidal silica grains, 10 mmol/liter ofsodium dodecyl sulfate used as an anionic surfactant, and the balance ofpure water was supplied through the supply pipe 3 onto the polishing pad2 at a rate of 12.5 ml/min so as to polish the copper film 36 and thebarrier layer 35 deposited on the silicon substrate 32 until the surfaceof the SiO₂ film 33 was exposed to the outside. It should be noted thatthe amount of hydrogen peroxide used was about 56 times as much byweight as the amount of 2-quinoline carboxylic acid used. In thispolishing step, etching of the copper film 36 was not recognized at allwhen the polishing solution was brought into contact with the copperfilm. Also, the polishing rate achieved by the polishing pad 2 was foundto be about 85 nm/min. As a result, the upper surfaces of theprojections of the copper film 36 as shown in FIG. 11B, which were in amechanical contact with the polishing pad 2, were preferentiallypolished first and, then, the exposed barrier layer 35 was subsequentlypolished. In other words, a so-called etch back was achieved. Since thepolishing was performed until the upper surfaces of the projectedportions of the SiO₂ 33 were exposed to the outside, formed was a coppervia fill 37 within the via hall 34, as shown in FIG. 11C. It is seenthat the copper via fill 37 was surrounded by the barrier layer 35, andthat the upper surface of the copper via fall 37 was flush with theupper surface of the SiO₂ film 33.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the copper viafall 37 was brought into contact with the polishing solution. However,the copper via fall 37 was found not to be etched at all. Further, thesilicon substrate having the copper via fall 37 formed therein wassubjected to an ultrasonic wave washing by using a pure water so as toclean the surface of the SiO₂ film 33.

In the next step, a Si₃ N₄ film 38 having a thickness of, for example,800 nm and acting as a second interlayer insulating film was formed by aCVD method on the surface of the SiO₂ film 33 including the copper viafall 37, as shown in FIG. 11D. Then, a plurality of trenches 39 eachhaving a depth of 400 nm and corresponding in shape to a wiring layerwere formed in the Si₃ N₄ film 38 by a photoetching technique such thatthese trenches 39 extended in a vertical direction to reach a middlepart of the Si₃ N₄ film 38, followed by forming a through-hole 40 by aphotoetching technique in one of these grooves to expose the copper viafall 37 formed previously. Further, a copper film 41 having a thicknessof 900 nm was formed by a sputtering technique on the surface of the Si₃N₄ film 38 including the trenches 39 and the through-hole 40, as shownin FIG. 11E.

The silicon substrate having the copper film 41 formed thereon as shownin FIG. 11E was held by the substrate holder 5 included in the polishingapparatus shown in FIG. 1 such that the copper film 41 was in contactwith the polishing pad 2, i.e., SUBA 800, included in the polishingapparatus. Under this condition, a load of 300 g/cm² was applied via thesupporting shaft 4 of the substrate holder 5 to the substrate in contactwith the polishing pad 2 disposed on the turntable 1, and the turntable1 and the substrate holder 5 were rotated in opposite directions each ata speed of 100 rpm. During the rotation, a polishing solution of thecomposition described previously was supplied through the supply pipe 3onto the polishing pad 2 at a rate of 12.5 ml/min so as to polish thecopper film 41 deposited on the silicon substrate 32 until the surfaceof the Si₃ N₄ film 38 was exposed to the outside.

It should be noted that the upper surfaces of the projections of thecopper film 41 as shown in FIG. 1E, which were in a mechanical contactwith the polishing pad 2, were preferentially polished to achieve aso-called etch back. Since the polishing was performed until the uppersurfaces of the projected portions of the Si₃ N₄ film 38 were exposed tothe outside, formed was a buried copper wiring layer 42 within each ofthe trenches 39 and the through-hole 40, as shown in FIG. 11F.Naturally, the copper wiring layer 42 thus formed within thethrough-hole 40 was in direct contact with the copper via fall 37 formedpreviously. It is seen that the upper surface of the buried copperwiring layer 42 was flush with the upper surface of the Si₃ N₄ film 38.

After the polishing treatment, the load applied to the polishing pad 2via the substrate holder 5 was released. Also, rotations of theturntable 1 and the holder 5 were stopped. As a result, the buriedcopper wiring layer 42 was brought into contact with the polishingsolution. However, the copper wiring layer 42 was found not to be etchedat all.

To reiterate, a multi-layer wiring structure comprising first and secondinterlayer insulating films 33, 39, the copper via fall 37 and buriedcopper wiring layer 42 formed in these interlayer insulating films,respectively, is employed in the semiconductor device prepared inExample 6. As already described, the upper surface of the copper viafall 37 is flush with the upper surface of the first interlayerinsulating film 33. Also, the upper surface of the copper wiring layer42 is flush with the upper surface of the second interlayer insulatingfilm 38. Naturally, the produced semiconductor device has a flatsurface.

As described above in detail, the present invention provides acopper-based metal polishing solution which does not dissolve at allcopper or a copper alloy when a copper or copper alloy film is immersedtherein and which permits polishing the copper or copper alloy film at apractical rate in the polishing step.

The present invention also provides a method for manufacturing asemiconductor device, comprising the steps of forming at least onemember selected from the group consisting of a trench and an opening inan insulating film formed on a surface of a semiconductor substrate,depositing a wiring material film consisting of copper or a copper alloyon the insulating film, and subjecting the deposited wiring materialfilm to an etch back in a short time so as to form a buried wiring layermade of copper or a copper alloy. It is important to note that the uppersurface of the buried wiring layer is made flush with the upper surfaceof the insulating film, with the result that the manufacturedsemiconductor device has a flat surface.

The present invention further provides a method for manufacturing asemiconductor device having a flat surface and exhibiting an excellentbreakdown voltage. The method comprises the steps of forming at leastone member selected from the group consisting of a trench and an openingin an insulating film formed on a surface of a semiconductor substrate,depositing a wiring material film consisting of copper or a copper alloyon the insulating film, and subjecting the deposited wiring materialfilm to an etch back in a short time so as to form a buried wiring layermade of copper or a copper alloy. It is important to note that the uppersurface of the buried wiring layer is made flush with the upper surfaceof the insulating film. In addition, the insulating film having theburied wiring layer formed therein is prevented from being thinned inthe etch back step.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method for manufacturing a semiconductordevice, comprising the steps of:forming at least one member selectedfrom the group consisting of a trench and an opening, said trench andopening conforming in shape with a wiring layer, in an insulating filmformed on a semiconductor substrate; forming a wiring material selectedfrom the group consisting of elemental copper and a copper alloy on saidinsulating film having at least one of said trench and opening formedtherein; and polishing the formed wiring material film until a surfaceof the insulating film is exposed by using a liquid polishingcomposition comprising a water-soluble organic acid capable of reactionwith copper to form a copper complex compound which is unlikely to bedissolved in water and has a mechanical strength lower than that ofcopper abrasive grains and water, thereby forming a buried wiring layerin the insulating film such that surfaces of the wiring layer and theinsulating film are level with each other.
 2. The method according toclaim 1, wherein a barrier layer is formed on said insulating filmbefore the step of forming at least one member selected from the groupconsisting of a trench and an opening.
 3. The method according to claim2, wherein said barrier layer is formed of a material selected from thegroup consisting of TiN, Ti, Nb, W and CuTa alloy.
 4. The methodaccording to claim 1, wherein said copper alloy is selected from thegroup consisting of a Cu--Si alloy, a Cu--Al alloy, a Cu--Si--Al alloy,and a Cu--Ag alloy.
 5. The method according to claim 1, wherein saidorganic acid contained in said liquid polishing composition is2-quinoline carboxylic acid.
 6. The method according to claim 1, whereinsaid organic acid is contained in said liquid polishing composition inan amount of at least 0.1% by weight.
 7. The method according to claim1, wherein said organic acid is contained in said liquid polishingcomposition in an amount of 0.3 to 1.2% by weight.
 8. The methodaccording to claim 1, wherein said abrasive grains contained in saidliquid polishing composition are formed of at least one materialselected from the group consisting of silica, zirconia, cerium oxide andalumina.
 9. The method according to claim 1, wherein said abrasivegrains contained in said liquid polishing composition have an averagegrain diameter of 0.02 to 0.1 μm.
 10. The method according to claim 1,wherein said abrasive grains are contained in said liquid polishingcomposition in an amount of 1 to 20% by weight.
 11. The method accordingto claim 1, wherein said liquid polishing composition further comprisesa promoter for forming a copper complex compound.
 12. The methodaccording to claim 11, wherein an oxidizing agent is used as saidpromotor for forming a copper complex compound.
 13. The method accordingto claim 12, wherein said oxidizing agent is hydrogen peroxide.
 14. Themethod according to claim 12, wherein said oxidizing agent is used in anamount at least 10 times as much by weight as the amount of saidwater-soluble organic acid contained in said liquid polishingcomposition.
 15. The method according to claim 1, wherein said liquidpolishing solution further comprises a surfactant.
 16. The methodaccording to claim 15, wherein said surfactant is an anionic surfactant.17. The method according to claim 15, wherein said surfactant is addedin an amount of at least 1 mol/liter.
 18. The method according to claim1, wherein said organic acid contained in said liquid polishingcomposition is 2-quinoline carboxylic acid, 2-pyridine carboxylic acid,2,6-pyridine carboxylic acid or a quinone.
 19. A method formanufacturing a semiconductor device with formed multilayerinterconnection structure, comprising the steps of:forming a firstopening corresponding to a first via fill in a first insulating film ona semiconductor substrate; forming a first wiring material filmconsisting of copper or a copper alloy on said first insulating filmincluding said first opening:polishing said first wiring material filmby using a first liquid polishing composition comprising a firstwater-soluble organic acid capable of reaction with copper to form acopper complex compound which is unlikely to be dissolved in water andhas a mechanical strength lower than that of copper, abrasive grains andwater, thereby forming said first via fill in said first opening;forming a second insulating film on said first insulating film includingsaid first wiring layer; forming a second opening corresponding to ashape of a second via fill in said second insulating film; forming asecond wiring material film consisting of copper or a copper alloy ofsaid second insulating film including said second opening; and polishingsaid second wiring material film by using a second liquid polishingcomposition having the same composition as said first liquid polishingcomposition, thereby forming a second via fill in said second opening.20. The method according to claim 19, wherein said organic acid is2-quinoline caboxylic acid.
 21. The method according to claim 19,wherein said first liquid polishing composition and said second liquidpolishing composition each further comprises a promoter for forming acopper complex compound.
 22. The method according to claim 19, whereinsaid first liquid polishing composition and said second liquid polishingcomposition each further comprises a surfactant.
 23. The methodaccording to claim 19, wherein a barrier layer is coated on the base andlateral face of said first opening after said forming of said firstopening and prior to said forming a first wiring material film.
 24. Themethod according to claim 23, wherein said barrier layer is made of atleast one material selected from the group consisting of TiN, Ti, Nb, Wand a CuTa alloy.
 25. The method according to claim 23, furthercomprising polishing said barrier layer except inside of said firstopening after polishing said first wiring material film.
 26. A methodfor manufacturing a semiconductor device with formed multilayerinterconnection structure, comprising the steps of:forming a firstopening corresponding to a first via fill in a first insulating film ona semiconductor substrate; forming a first wiring material filmconsisting of copper or a copper alloy on said first insulating filmincluding said first opening:polishing said first wiring material filmby using a first liquid polishing composition comprising a firstwater-soluble organic acid capable of reaction with copper to form acopper complex compound which is unlikely to be dissolved in water andhas a mechanical strength lower than that of copper, abrasive grains andwater, thereby forming said first via fill in said first opening;forming a second insulating film on said first insulating film includingsaid first via fill; forming a trench corresponding to a shape of asecond wiring layer in said second insulating film; forming a secondopening reached to said first via fill at the base of said secondopening in said second insulating film; forming a second wiring materialfilm consisting of copper or a copper alloy on said second insulatingfilm including said trench and said second opening; and polishing saidsecond wiring material film by using a second polishing compositionhaving the same composition as said first liquid polishing composition,thereby forming said second wiring layer and said second via fill insaid trench and said second opening.
 27. The method according to claim26, wherein said organic acid is 2-quinoline carboxylic acid.
 28. Themethod according to claim 26, wherein said first liquid polishingcomposition and said second liquid polishing composition each furthercomprises a promoter for forming a copper complex compound.
 29. Themethod according to claim 26, wherein said first liquid polishingcomposition and said second liquid polishing composition each furthercomprises a surfactant.
 30. The method according to claim 26, wherein adiffusion layer is formed on said semiconductor substrate, and saidfirst via fill is connected to said diffusion layer.
 31. The methodaccording to claim 26, wherein a barrier layer is coated on the base andlateral face of said first opening after said forming of said firstopening and prior to forming said first wiring material film.
 32. Themethod according to claim 31, wherein said barrier layer is made of atleast one material selected from the group consisting of TiN, Ti, Nb, Wand a CuTa alloy.
 33. The method according to claim 31, furthercomprising polishing said barrier layer except inside of said firstopening after polishing said first wiring material film.